In the past, large companies having a corporate headquarters and multiple branch offices have tended to operate independent self-contained telecommunication systems at each of the branches and at the headquarters. Naturally, these independent systems would be networked together. The administrative effort and the costs involved in running such multiple independent systems was high.
More recently, by using Internet Protocol (IP) internetworking between the headquarters and the various branches, it has been possible to relocate parts of the headquarters central system into the branches, whilst retaining a single point of control at the headquarters.